Dry type transformer

[GoldDigger]

If the nameplate is correct, you cannot use wye-wired loads on the high voltage side. Period!
If it were not for that problem, all you would have to do is change the taps on the high voltage side to lower the voltage.
Since the taps are on the secondary side in this configuration they cannot serve to prevent core saturation from excessive primary voltage.

 

[packersbay]

I'm thinking that if there is a 480Y/277 volt panel feeding the lighting the nameplate in post #30 is not the correct one

Panel is 480v/277v, when I power down that trans I lose voltage to panel.

 

[hillbilly1]

I agree with the others, you do not have a 277 volt tap. Normally with that set up, you would have one phase grounded, or a fault monitor. If your phase to phase voltage is too high, then the 208 volt side can be tapped higher to lower the output voltage. Your lights are most likely 480 volt HID ballast loads, not 277.

 

[hillbilly1]

Oops! Sorry! Being backfeed, the voltage taps are on the output side!

 

[Tulsa Electrician]

If you shut down the trans and panle get a few pics. I'm interested to see how they derived the netural.

 

[kwired]

If you shut down the trans and panle get a few pics. I'm interested to see how they derived the netural.

If load is well balanced it would be able to operate at ~277 volts to the "floating neutral" but is a little hard to believe it is balanced that well, especially when ballast/drivers start going out from over voltage.

A wye wound motor does exactly what I described, the wye point floats but the current is equal on all three phase conductors so voltage to that floating neutral remains pretty constant from all three.

 

[LarryFine]

And the primary neutral should be left floating in this instance, yes?

 

[GoldDigger]

And the primary neutral should be left floating in this instance, yes?

Absolutely. Otherwise risk of damaging circulating currents in both primary neutral and secondary windings.

 

[hillbilly1]

Looks like an oops!, the original transformer was installed incorrectly, and the neutral bar just has the egc ran to it. Panel should have been labeled 480 volt only. Either the transformer will need to be changed, or the new LED’s changed out to 480. (Third option, 480 adapter at each fixture. One manufacturer used a multi tap ballast, using the lower volt tap as an auto transformer. This was before they made 480 volt drivers.)

 

[hillbilly1]

There is a fourth option, the transformer could be bypassed, fixtures ran on 120 or 208 if the are auto volt, providing existing circuiting is large enough. The main to the transformer would need to be reduced also to the rating of the panel. Being LED, this should work, and you wouldn’t have the transformer loss either.

 

[synchro]

It would be a kludge, but the OP's equal L-N measurements could be explained if a neutral was being derived by an additional wye-delta acting as a grounding transformer. For example, this could be made from a 480V delta/ 480V wye by connecting its wye side windings to the 3-wire 480V output of the posted transformer.

 

[Tulsa Electrician]

I'm waiting on pics and one line.

 

[ptonsparky]

I'm waiting on pics and one line.

Don't forget to breathe.

 

[packersbay]

I'm waiting on pics and one line.

Not onsite at the moment

 

[augie47]

Do you know where the neutral was connected in the transformer ?

 

[Tulsa Electrician]

Not onsite at the moment

No rush
I think you have a good idea on what may be happening. If that is the case it should be resolved as it is a danger issue.
Glad you ask.

 

[Tulsa Electrician]

Don't forget to breathe.

Priceless
Nice one. I needed that.

 

[NewtonLaw]

Best solution, https://surplusrecord.com/view-all-listings/?cat_id=36314, A selection of 45 kVA units with a 208 volt primary Delta and 480Y/277 volt secondary.